Heretofore, the prior art has, in the main, suggested the use of strictly pneumatically operated fuel bowl vent means for carburetors or the like. Such prior art pneumatically operated fuel bowl vent means are arranged as to be responsive to engine or intake manifold vacuum. That is, the vent means is intended to be closed during all conditions of engine operation because of the existance of associated engine or intake manifold vacuum. Upon engine shut-down, associated biasing spring means serves to open the venting means. However, it has been found that such prior art pneumatic venting systems fail to provide operating characteristics which satisfy engine operating requirements. That is, such prior art pneumatic venting systems open whenever engine or manifold vacuum is low during engine operation such as during, for example, near or at wide open throttle operation. During this time the very low manifold vacuum available to keep the venting system closed is insufficient to overcome the reverse force of the biasing spring means tending to open the venting system. Consequently, such opening of the venting means, during such segments of engine operation, results in a change in the fuel metering pressure differential across the fuel within the fuel reservoir thereby increasing (from a desired rate) the rate of metered fuel flow to the engine (since air cleaner depression increases the total metering differential pressure across the carburetor) and deleteriously effecting engine operation and performance.
Accordingly, the invention as herein disclosed and claimed is primarily directed to the solution of the preceding as well as other related and attendant problems.